1. Field of the Invention
In moving vehicle tracking systems, and especially in spacecraft tracking systems, wherein the vehicle changes attitude, or position, relative to the base station, it is often difficult to maintain a direct transmission path to an antenna mounted on the vehicle. To overcome this problem several antennas are normally mounted on the vehicle in spaced-apart positions so that at least one antenna is in communication with the base station at all times and regardless of the attitude or position of the vehicle. However, another problem arises because the antennas are spaced apart. Because the antennas are at different distances from the base station, the phase of the signals received at the antennas differs substantially. Decision-making apparatus typically is required to select which of the several received signal phases will be used to control the frequency and phase of the transmitted signal.
2. Description of the Prior Art
In prior art systems a single receiver is generally used with the plurality of antennas and a switching system is incorporated between the receiver and the antennas so that the antenna receiving the strongest signal is connected to the receiver and the remaining antennas are disconnected. As the vehicle maneuvers the switching systems switches antennas and, because of the switching function and the fact that the antennas are receiving signals of different phases, the composite signal applied to the receiver may contain discontinuities as well as spikes and the like caused by the switching functions. These discontinuities, spikes, etc., cause the system to lose coherence with a resultant loss in transmitted information.